This project consists of three studies. Two cross-sectional studies will be used to test alternative models of the underlying dimensions of individual differences in vocabulary and in fluency, respectively. The goal of study one is to examine two potential dimensions of vocabulary knowledge. The first is a distinction between producing a definition and using a word in context. The second is a contrast between vocabulary knowledge and morphological awareness. The goal of study two is to understand what roles accuracy and rate play in both reading and rapid naming. This study will examine the relation between reading rate and accuracy, as well as between rapid naming rate and rapid naming accuracy, using a confirmatory factor analysis with multiple measurements of the constructs to create latent variables. This study will address the extent to which individual differences in accuracy and rate when reading passages for comprehension are indicators of (a) the identical construct of reading skill, (b) distinct yet correlated constructs, (c) independent constructs, or (d) negatively correlated constructs because of speed-accuracy tradeoffs. The study also will address these same four possibilities for speed and accuracy in the rapid naming task. In addition, the study will address the relation between speed and accuracy measured in the context of reading passages for comprehension and in the context of rapid naming tasks. Participants in the first two studies will be 100 second-grade and 100 fourth-grade children respectively. Participants in a follow-up longitudinal study will be 300 first-grade students who will be assessed annually through fourth grade. This study will serve to test alternative models of developing causal relations among nine key constructs: phonological awareness, decoding, vocabulary-including morphological aspects, fluency, reading comprehension, spelling, written expression, working memory, and listening comprehension.